1. Field of the Invention
The present invention relates to a distributed base station/repeating unit in a mobile communication system, and more particularly to a distributed multi-drop base station/repeating unit using an extension of analog optical transmission in a mobile communication system, wherein a larger number of remote units or repeaters are cascaded to a base station, which is a main unit, in such a manner that they minimize attenuation and loss of an optical signal, thereby enabling a mobile communication service to be more efficiently provided over a wider area.
2. Description of the Related Art
As well known to those skilled in the art, mobile communication service providers recognize the extension of base station service coverages of mobile communication systems as a very important factor from an economical or technical point of view. Note that base station service coverages are extended differently according to given environments such as a downtown area, rural district, etc., which have a great effect on base station installation and management costs. In this regard, mobile communication service providers are focusing their studies on a more efficient extension of base station service coverages.
In order to eliminate propagation shadow regions or extend base station service coverages, conventional mobile communication systems have employed methods using distributed base stations and methods using repeaters. The methods using repeaters may be roughly classified into a method using a microwave, a method using a radio frequency (RF) and a method using digital or analog optical transmission. A representative example of the methods using distributed base stations may be a method using digital or analog optical transmission. Because the present invention is applied to a scheme using analog optical transmission, a description will hereinafter be given of only a conventional technique using the optical transmission scheme.
FIG. 1 is a functional block diagram showing the construction of a conventional distributed base station/repeating unit using analog optical transmission. As shown in this drawing, optical couplers 3 are used to cascade a plurality of remote units or repeaters 2 to a main unit 1, which is a base station, on a sector basis. A first one of the optical couplers 3 acts to receive an optical signal from the main unit 1, split the received optical signal into two signals and supply one of the two signals to a first one of the remote units or repeaters 2 at the same time that the other is supplied to a second one of the optical couplers 3 connected to a second one of the remote units or repeaters 2.
However, in the above-mentioned conventional distributed base station/repeating unit using analog optical transmission, an optical signal transmitted from the main unit is split by the optical couplers and then transferred to the remote units or repeaters, so it suffers severe attenuation. Besides, a transmission/reception noise figure resulting from an optical transducer and optical cable is so high as to degrade a reception characteristic. For this reason, optical transmission distances between the main unit and two or more remote units or repeaters are shortened, resulting in distance restrictions when the two or more remote units or repeaters are cascaded to the main unit. With the optical transmission distances between the main unit and the remote units or repeaters being shortened, a mobile communication service cannot be provided to a subscriber located at an out-of-the-way tourist resort or a seaside place far away from the main unit. In a mobile communication service provider's situation, a larger number of base stations, each of which is the main unit, must be installed, increasing an economic burden on the mobile communication service provider and, in turn, resulting in difficulty in technically managing the base stations.